1. Field of the Invention
The present invention relates to an air-conditioning system in a vehicle, and particularly, to an air-conditioning system for an electric vehicle, comprising a heat pump type system having an interior heat exchanger and an exterior heat exchanger, so that air-cooling and heating are conducted by circulating a refrigerant between these interior and exterior heat exchangers while producing a change in phase between gas and liquid phases.
2. Description of the Prior Art
In general, an air-cooling system in a vehicle is comprised of an evaporator as an interior heat exchanger for heat exchange with air supplied into a passenger compartment, a condenser as an exterior heat exchanger for heat exchange with the open air taken from the outside of the vehicle, a compressor for compressing a refrigerant flowing from the evaporator to the condenser, and a depressurizing means such as an expansion valve for depressurizing the refrigerant flowing from the condenser to the evaporator.
In such air-cooling system, a refrigerating cycle is carried out in the following manner: first, a gas phase refrigerant compressed by the compressor is passed at a high temperature and a high pressure into the condenser. The open air is blown through the condenser by a cooling fan, so that the refrigerant is cooled and liquefied by such open air. The liquefied high pressure refrigerant is then depressurized by the expansion valve and fed to the evaporator. In this evaporator, the refrigerant is vaporized by absorbing heat from the surroundings. Thus, if air is introduced from the outside of the vehicle or from the passenger compartment and supplied into the compartment through the evaporator, such air is cooled to effect the cooling of the compartment. Then, the vaporized refrigerant is fed again to the compressor, where it is compressed.
The complete air-conditioning for a vehicle with an internal combustion engine is constructed by a combination of a vapor-compressing type cooling system for performing such a refrigerating cycle and a separate heater utilizing engine-cooling water.
Recently, it has been increasingly proposed to employ a heat pump system for the entire air-conditioning for the vehicle, as described in, for example, Japanese Patent Application Laid-open No. 17932285. An interior heat exchanger and an exterior heat exchanger are mounted in such a heat pump type air-conditioning system, so that the air-cooling is carried out by circulating a refrigerant between these heat exchangers in the same manner as in the above-described refrigerating cycle. The air heating is carried out by changing-over the direction of flow of the refrigerant and reversing the refrigerating cycle so as to release heat from the interior heat exchanger.
With such a heat pump type air-conditioning system, heat is absorbed from the open air to provide the air-heating and hence, the start of the air-heating begins immediately without waiting for the engine cooling water to become heated. Such heat pump type air-conditioning is also applicable to an electromobile equipped with no internal combustion engine.
In this way, the interior and exterior heat exchangers are used in either mode of operation of the vapor-compressing or heat pump type of air-conditioning. The interior heat exchanger is disposed inside the passenger compartment, because it provides heat exchange with the air supplied into the compartment. The exterior heat exchanger normally is disposed adjacent a radiator within an engine room located at the front end of the vehicle body, which makes it easy to supply air from outside of the vehicle, because it provides heat exchange with the open air. Usually, the engine room in which the exterior heat exchanger is placed is partitioned, by a dashboard, from the compartment in which the interior heat exchanger is placed.
In the prior art air-conditioning for the vehicle, the compressor is disposed within the engine room, because it is driven by the internal combustion. The exterior heat exchanger is also disposed within the engine room, as described above. In other words, the exterior heat exchanger and the compressor are disposed in the same chamber, as also described in the above-described patent.
However, the inside of the engine room is heated to a high temperature by the generation of heat from the engine and the like. The compressor itself also generates heat. For this reason, if the exterior heat exchanger is placed in the same chamber as are the heat generating sources such as the engine and the compressor, it is subjected to radiant heat from these heat generating sources. In addition, the cooling efficiency of the compressor is reduced and hence, when the refrigerant is compressed to a predetermined pressure by the compressor, it is heated more than necessary. Therefore, in order to conduct the air-cooling operation, it is necessary to use an exterior heat exchanger of a larger capacity to exhibit an increased cooling capability.
This will be described with respect to a Mollier diagram. The above-described refrigerating cycle is as shown in FIG. 10. More specifically, if the refrigerant is compressed by the compressor, the temperature and pressure of the refrigerant are changed from a point a to a point b in FIG. 10. They are changed from the point b to a point c in FIG. 10 by releasing heat from the exterior heat exchanger. Further, they are changed from the point c to a point d in FIG. 10 by depressurization of the refrigerant by the expansion valve. They are returned from the point d to the point a by absorption of heat by the refrigerant through the interior heat exchanger.
During this time, the compressor is not sufficiently cooled because the temperature of the air flowing around the compressor is higher, and hence, when the refrigerant is compressed to the predetermined pressure, the temperature of the refrigerant is at temperature at a point b' higher than the point b. Therefore, in order to lower the temperature of the refrigerant down to the point c, a corresponding increased capacity is required for the exterior heat exchanger. Moreover, the efficiency of the exterior heat exchanger is reduced by reception of radiant heat from the compressor, engine and the like and hence, it is necessary to further increase the capacity of the exterior heat exchanger. Additionally, the compressor performs additional work in raising the temperature of the refrigerant up to the point b' and therefore, the efficiency of the compressor itself is also reduced.
The energy consumed during air-cooling conducted for the air-conditioning of the vehicle is extremely large and a problem, particularly in the case of an electromobile, wherein the electrical power quantity is limited. For this reason, when the electric power quantity is consumed by the air-cooling, the travellable distance of the electric vehicle may be shortened. Thus, improvement in the air-cooling efficiency is an important consideration.